1. Field of the Invention
The present invention relates to a technique for estimating the motion amount of an interlaced video signal.
2. Description of the Related Art
Currently, typical video signal processing apparatuses handle interlace-scanned image signals.
Flicker commonly occurs in horizontal edge portions of an interlace-scanned image. As a means for addressing this problem, a technique is known in which interpolation is performed on interlace scan lines so as to generate and output a progressive-scan image signal.
Also, a technique is known in which, when converting into progressive scanning, the motion amount of an image is estimated, and the signal of a previous field and that of a current field are combined according to the result of the motion estimation to generate an interpolation signal. According to this technique, the condition of the interpolation signal varies according to the accuracy of the result of the motion estimation.
For example, if interpolation is performed with the image signal of a current field for a still area, narrow horizontal stripes disappear, causing a flicker. Conversely, if interpolation is performed with the image signal of a previous field for a moving area, a motion blur occurs, causing combing noise.
A technique for increasing the accuracy of motion estimation results is disclosed in Japanese Patent Laid-Open No. 2006-41619. According to this document, a pixel is selected from the upper and lower lines located above and below a pixel for interpolation. Using the differences between calculated results of these pixels and a pixel located in the same position as the pixel for interpolation in a previous field as an inter-field difference value, motion estimation is performed.
However, as shown in FIG. 2, when the pixels from the upper and lower lines are calculated, the following problem remains. That is, the pixels of a vertical line positioned at a high frequency area such as on a horizontal edge are blurred as compared to those of the same area of the actual frame. More specifically, because motion estimation is performed using a difference in values between the computed result and the pixel located in the same position as the pixel for interpolation in the previous field, motion amount is likely to be determined even for a still area, and line flicker therefore occurs.